Projectile Motion (Galileo and Newton) Documents

Main Document

The EJS Projectile Motion (Galileo and Newton) Model presents two different views of projectile motion. The first view, associated with Galileo, describes projectile motion as a combination of horizontal motion with a constant velocity, equal to the projectile initial horizontal velocity component, and vertical motion with constant acceleration and an initial velocity equal to the projectile's initial vertical velocity component. The second view, described by Newton in his Principia, presents projectile motion as a combination of inertial motion, with constant velocity equal to the projectile's initial velocity, and motion produced by a constant downward acceleration starting from rest. These two views are mathematically equivalent, but each view emphasizes different aspects of the motion.

The simulation shows the motion of the projectile for a given initial height, launch speed, and launch angle (all of which can be selected using the simulation controls). Optionally, the simulation will display the velocity of the projectile, as well as the velocity components (horizontal and vertical for the Galileo view, inertial and forced for the Newton view). The simulation can also show a series of "ghosts" - images showing the location and velocity of the projectile at regular intervals of time. Finally, the simulation can display a series of lines that illustrates how the two different types of motion combine to produce the overall trajectory of the projectile.

By default the view is scaled to fit the entire trajectory, as well as any ghosts, within the window. This generally means that the horizontal and vertical distances are not shown to the same scale, which can lead to distortions in the shape of the projectile and other similar effects. The user has the option to square the display (see below) to remove these effects, although this may result in the visual elements occupying only a small portion of the viewing window.